Benzene, Toluene, Ethylbenzene And P-xylene Research Articles

Efficient capture of benzene and its homologues volatile organic compounds with protic [MIM][NTF2] and aprotic [EMIM][NTF2] ionic liquids: Experimental and computational thermodynamics

Using new green solvents to effectively capture volatile organic compounds (VOCs) is considered as an attractive green sustainable chemical development route. In this work, benzene, toluene, ethylbenzene and p-xylene (BTEX) were selected as typical aromatic VOCs. The gas absorption performance of proton [MIM][NTF2] and aprotic [EMIM][NTF2] ionic liquids (ILs) for BTEX were studied by computational thermodynamics combined with gas absorption experiments. Absorption experiments of BTEX and regeneration experiments of ILs were carried out at different temperatures, and ILs had good stability. The interaction type and intensity were determined by Interaction Region Indicator (IRI) analysis of IL-BTEX blend systems. The C-H···π and π-π interaction between imidazole ring and BTEX were the direct reason why ILs can efficiently absorb BTEX. Molecular dynamics simulations were performed to explore the diffusion behavior of gas in ILs. The increase of methyl group increases the interaction strength of the system, and the fractional free volume of IL-BTEX blend systems decreases gradually, which limits the diffusion of BTEX. Non-bond interaction analysis shows that van der Waals interaction was the main driving force of BTEX absorption in ILs.

Health Risk Assessment of the Levels of BTEX in Ambient Air of One Urban Site Located in Leon, Guanajuato, Mexico during Two Climatic Seasons

Levels of BTEX (benzene, toluene, ethylbenzene, and p-xylene) were determined in ambient air of an urban site located at the center of Mexico (Leon City in Guanajuato State) during two climatic seasons of 2018 (summer and autumn). Ethylbenzene (11.86 µg m−3) and toluene (11.85 µg m−3) showed the highest median concentrations during the study period. BTEX concentrations did not show a diurnal pattern but a seasonal trend was observed for benzene and toluene at a significant level of α = 0.05. Bi-variate and multivariate analysis showed significant positive correlations (at α = 0.05) among BTEX (excepting benzene), indicating common sources for toluene, ethylbenzene, and p-xylene and a different origin for benzene. A meteorological study was also conducted in order to determine the origin of air masses that could influence the BTEX concentrations in the study site. Finally, it was found that all BTEX species presented hazard quotient values (HQs) <1, indicating that there is no risk of non-cancer during the studied period. Lifetime cancer risk due to benzene exposure for the adult and child populations studied were estimated to be 7 in 1,000,000 and 1 in 100,000, respectively.

A green adsorbent for the removal of BTEX from aqueous media

Ostrich bone waste (OBW) was modified chemically with citric acid and used as a bioadsorbent. The uptake of benzene, toluene, ethylbenzene, andp-xylene (BTEX) and the adsorption mechanism of BTEX by the green adsorbent (OBW-NaOH–CA) were studied.

Removal of BTEX by using a surfactant – Bio originated composite

The application of ostrich bone waste-loaded a cationic surfactant (OBW-OH-CTABr) bioadsorbent for benzene, toluene, ethylbenzene and p-xylene (BTEX) removal from the synthetic and real waters have been studied, and the prepared biomaterials were studied by Fourier transform infrared (FTIR), X-ray diffraction (XRD), surface area measurements (BET), scanning electron microscopy (SEM), Energy-dispersive X-ray spectroscopy (EDX) and point of zero (pHPZC). The immobilization of CTABr molecules on the framework of modified OBW showed good tendency to adsorb BTEX from aqueous solution. The exposure time to obtain equilibrium for maximum removal of BTEX was observed to be 60min. The removal kinetics of BTEX has been evaluated in terms of pseudo-first- and -second-order kinetics, and the Freundlich and Langmuir isotherm models have also been utilized to the equilibrium removal data. The removal process was spontaneous and endothermic in nature and followed pseudo-second-order kinetic model. The immobilized CTABr showed high reusability because of its high adsorption efficiency after 12th cycles. The proposed low-cost bioadsorbent could also be utilized to adsorb BTEX from the real water (Anzali lagoon water). The OBW-OH-CTABr composite is indeed an attractive biomaterial for drinking water-based pollutants and act as an adsorbent for BTEX and oil spills especially in third world due to its low-cost preparation and regeneration and clean processing of the biomaterial with no byproducts after utilize.

Occurrence of volatile organic compounds in shallow alluvial aquifers of a Mediterranean region: Baseline scenario and ecological implications

A regional survey of eight volatile organic compounds (VOCs), namely BTEX (benzene, toluene, ethylbenzene and p-xylene) and four chlorinated aliphatic hydrocarbons (CAHs: chloroform, 1,2-dichloroethane, trichloroethene and tetrachloroethene), was carried out at 174 sites, in 17 alluvial aquifers of Abruzzo, a Mediterranean region of southern Italy, from 2004 to 2009. Frequency of detection, concentration range, spatial distribution pattern, and temporal trend of contaminant concentration in each aquifer were analyzed as well as the relationships between VOC concentrations and the total amount of precipitation during the 90days preceding each sampling date. A review of published ecotoxicological data, providing an indication of the biological risk associated with the observed levels of VOC contamination, was presented and discussed. BTEX concentrations were under detection limits in all the investigated aquifers, indicating absence of contamination. In contrast, CAH contamination occurred in 14 out of 17 aquifers. The two most frequently detected compounds were chloroform and tetrachloroethene. No significant temporal trend was observed for chloroform and tetrachloroethene concentrations during the six years of observation, indicating the persistence of stable contaminations, except for some slightly decreasing trends observed in three out of 17 aquifers. In four aquifers chloroform and tetrachloroethene concentrations increased with precipitations in the preceding months. Spatial patterns of contamination differed among aquifers, indicating highly complex contaminant distributions at aquifer scale not related to single-plume geometries. Patterns of contamination by chloroform and tetrachloroethene in the most urbanized aquifers were likely associated with multiple sources of VOCs not clearly detectable at the scale used in this study. In five out of 17 aquifers, chloroform and tetrachloroethene co-occurred at concentrations that are lethal to groundwater-dwelling organisms under a short exposure period (four days). Future studies should therefore consider the possibility that in the other aquifers groundwater-dwelling organisms might be physiologically damaged by sublethal VOC concentrations.

Removal of BTEX from aqueous solutions by paper mill sludge-based activated carbon

The removal of BTEX (benzene, toluene, ethyl-benzene and p-xylene) from contaminated groundwater was evaluated by paper mill sludge-based activated carbon, prepared by chemical activation and pyrolysis.The effects of pH, time, adsorbent dosage and adsorbate concentration were studied through batch adsorption experiments. Selected physical and chemical characteristics of the adsorbents, such as specific surface area (613m2/g), pore volume distribution (micropore: 277cm3/g, mesopore: 365cm3/g) and surface functional groups (carboxylic, alkyl and aliphatic groups) were determined by N2 adsorption-desorption diagram and FTIR, respectively. The removal efficiency of the four target compounds would be more than 92 %, which the initial concentrations of BTEX and the adsorbent dosage were 40 mg/l and 1000 mg/l, respectively. It was proved that pH and ionic strength have insignificant effects on the adsorption efficiency. The order of adsorption amount in all experiments was > ethyl-benzene > toluene > benzene. The kinetic data proved a closer fit to the pseudo-first-order model. The isotherm experimental data showed a better fit to either Freundlich or Langmuir model. In addition, a series of experiments was conducted to evaluate the capacity of the adsorbent in adsorbing the BTEX from a groundwater sample contaminated with gasoline.

The effect of the potential fuel additive isobutanol on benzene, toluene, ethylbenzene, and p-xylene degradation in aerobic soil microcosms

Isobutanol is being considered as a fuel additive; however, the effect of this chemical on gasoline degradation (following a spill) has yet to be fully explored. To address this, the current study investigated the effect of isobutanol on benzene, toluene, ethylbenzene and p-xylene (BTEX) degradation in 14 sets of experiments in saturated soils. This involved four hydrocarbons for three soils (12 experiments) and two extra experiments with a lower level of isobutanol (for toluene only). Each soil and hydrocarbon combination involved four abiotic control microcosms and 12 sample microcosms (six with and six without isobutanol). The time for complete degradation of each hydrocarbon varied between treatments. Both toluene and ethylbenzene were rapidly degraded (5–13 days for toluene and 3–13 days for ethylbenzene). In contrast, the time for complete degradation for benzene ranged from 5 to 47 days. The hydrocarbon p-xylene was the most recalcitrant chemical (time for removal ranged from 14 to 86 days) and, in several microcosms, no p-xylene degradation was observed. The effect of isobutanol on hydrocarbon degradation was determined by comparing degradation lag times with and without isobutanol addition. From the 14 treatments, isobutanol only affected degradation lag times in three cases. In two cases (benzene and p-xylene), an enhancement of degradation (reduced lag times) was observed in the presence of isobutanol. In contrast, toluene degradation in one soil was inhibited (increased lag time). These results indicate that co-contamination with isobutanol should not inhibit aerobic BTEX degradation rates.

A permeable reactive barrier for the bioremediation of BTEX-contaminated groundwater: Microbial community distribution and removal efficiencies

This study was conducted with column experiments, batch experiments, and bench-scale permeable reactive barrier (PRB) for monitoring the PRB in the relation between BTEX (benzene, toluene, ethylbenzene, and p-xylene) decomposition efficiency and the distribution of a microbial community. To obtain the greatest amount of dissolved oxygen from oxygen-releasing compounds (ORCs), 20-d column tests were conducted, the results of which showed that the highest average amount of dissolved oxygen (DO) of 5.08 mg l(-1) (0.25 mg-O(2)d(-1)g(-1)-ORC) was achieved at a 40% level of CaO(2). In the batch experiments, the highest concentrations of benzene and toluene in which these compounds could be completely degraded were assumed to be 80 mg l(-1). Long-term monitoring for a PRB indicated that ORCs made with the oxygen-releasing rate of 0.25 mg-O(2)d(-1)g(-1)-ORC were applicable for use in the PRB because these ORCs have a long-term effect and adequately meet the oxygen demand of bacteria. The results from the DGGE of 16S rDNAs and real-time PCR of catechol 2,3-dioxygenase gene revealed the harmful effects of shock-loading on the microbial community and reduction in the removal efficiencies of BTEX. However, the efficiencies in the BTEX decomposition were improved and the microbial activities could be recovered thereafter as evidenced by the DGGE results.

Surface modification of carbon nanotubes for enhancing BTEX adsorption from aqueous solutions

Carbon nanotubes (CNTs) were fabricated by the catalytic chemical vapor deposition method and oxidized by HCl, H 2SO 4, HNO 3 and NaOCl solutions for enhancing benzene, toluene, ethylbenzene and p-xylene (BTEX) adsorption in an aqueous solution. The surface nature of CNTs was changed after the H 2SO 4, HNO 3 and NaOCl oxidation, which makes CNTs that adsorb more BTEX. The NaOCl-oxidized CNTs show the greatest enhancement in BTEX adsorption, followed by the HNO 3-oxidized CNTs, and then the H 2SO 4-oxidized CNTs. The adsorption mechanism of BTEX via CNTs is mainly attributed to the π–π electron-donor–acceptor interaction between the aromatic ring of BTEX and the surface carboxylic groups of CNTs. The NaOCl-oxidized CNTs have superior adsorption performance of BTEX as compared to many types of carbon and silica adsorbents reported in the literature. This suggests that the NaOCl-oxidized CNTs are efficient BTEX adsorbents and that they possess good potential applications for BTEX removal in wastewater treatment.

Simultaneous determination of gasoline oxygenates and benzene, toluene, ethylbenzene and xylene in water samples using headspace-programmed temperature vaporization-fast gas chromatography–mass spectrometry

A sensitive method is presented for the fast analysis of seven fuel oxygenates (methanol, ethanol, tert-butyl alcohol (TBA), methyl tert-butyl ether (MTBE), ethyl tert-butyl ether (ETBE), tert-amyl methyl ether (TAME) and diisopropyl ether (DIPE)) and benzene, toluene, ethylbenzene and p-xylene (BTEX) in water samples. The applicability of a headspace (HS) autosampler in combination with a GC device equipped with a programmable temperature vaporizer (PTV) and a MS detector is explored. The proposed method achieves a clear improvement in sensitivity with respect to conventional headspace methods due to the use of the PTV. Two different packed liners with materials of different trapping strengths (glass wool and Tenax-TA) were compared. The benefits of using Tenax-TA instead of glass wool as packed material for the measurement of the 11 compounds emerged as better signal-to-noise ratios and hence better detection limits. The proposed method is extremely sensitive. The limits of detection are of the order of ng/L for six of the compounds studied and of the order of μg/L for the rest, with the exception of the most polar and volatile compound: methanol. Precision (measured as the relative standard deviation for a level with an S/N ratio close to 3) was equal to or lower than 15% in all cases. The method was applied to the determination of the analytes in natural matrixes (tap, river and sea water) and the results obtained can be considered highly satisfactory. The methodology has much lower detection limits than the concentration limits proposed in drinking water by the US Environmental Protection Agency (EPA) and the European Union for compounds under regulation.

Organic compound distribution between nonionic surfactant solution and natural solids: Applicability of a solution property parameter

A solution property parameter φ was defined to examine the distribution characteristics of organic compounds between the solids and four nonionic surfactant solutions. The studied compounds consisted of BTEX (benzene, toluene, ethylbenzene, and p-xylene) and chlorinated pesticides (lindane, α-BHC, and heptachlor epoxide), which span several orders of magnitude in terms of water solubility ( S w). The solid samples were composed of a very low organic matter clay (Ca-montmorillonite), and a high organic matter natural soil (Shamou Mountain soil). The surfactants tested included two alkyl chain surfactants and two containing aromatic group surfactants with added concentrations both below and above their critical micelle concentration (CMC). By observing the K om or K sf variation, the result indicates, besides the S w of the organic compounds, the distribution coefficient is regarded as a function of the soil organic matter (SOM) constituents, and the chemical structure of the organic compounds. Also, it can be found the greater φ values represent the higher releasing ratios of the organic compounds from the contaminated soil to groundwater. For the relatively higher S w compounds, such as BTEX, all of the φ values are close to 1. The φ values for the relatively lower S w compounds are far greater than 1, and increase with the increasing affinity of the compounds to the surfactants.

Nanoparticle and Nanoporous Carbon Adsorbents for Removal of Trace Organic Contaminants from Water

Removal of a wide range of trace organic contaminants from water to concentrations below USEPA Maximum Contaminant Levels (MCL) remains an important goal for the water industry. Design of advanced carbon based adsorption systems represents a unique approach to solving these problems. A number of successful examples are cited in this paper and are briefly summarized in the following section. (1) Removal of foulants such as humic acid using nanoparticle carbon blacks and chemically activated nanoporous fibers; (2) Removal of trace organic contaminants such as benzene, toluene, ethylbenzene and p-xylene (BTEX) to levels below USEPA MCL using nanoporous carbon fibers; (3) Removal of trace chemical warfare simulants such as diisopropylmethyl phosponate and chloroethylethylsulfide using enlarged nanoporous carbon fibers; (4) Removal of trace chlorinated solvents such as trichloroethylene (TCE) and chloroform using tailored nanoporous carbon fibers; (5) Removal of the trace herbicide, atrazine, to below USEPA MCL level using nanoporous chemically activated fibers. In this paper the enormous improvement of the above systems over commercially available products in static and dynamic adsorption evaluation is described.

The effect of surfactants on the distribution of organic compounds in the soil solid/water system

The efficiency of soil remediation by surfactant washing was evaluated via the measured distribution coefficients of a number of nonpolar compounds in several soil–water mixtures. The studied compounds (contaminants) are BTEX (benzene, toluene, ethylbenzene, and p-xylene) and three chlorinated pesticides (lindane, α-BHC, and heptachlor epoxide), which span several orders of magnitude in water solubility ( S w). A peat, and two natural soils were used that comprise a wide range in soil organic matter (SOM) content. The surfactants tested included cationic, anionic and nonionic types, with concentrations up to five to six times the critical micelle concentration (CMC). The K d * / K d , values were used to evaluate the remediation efficiency under various operation conditions. For relatively water soluble BTEX compounds, the surfactant adsorption on the soil surface is the deciding factor on contaminant desorption from soil. For the less-soluble pesticides, surfactant micelles in solution influence the contaminant desorption more. The contaminants partitioning to SOM or adsorbed surfactants lowers the desorption efficiency. Anionic surfactants are found to be a better choice on soil remediation because they do not form admicelle on soil surface that enhances the SOM content. Cationic surfactant, which adsorb onto soil surfaces, leads to poor remediation efficiency. An improper selection of surfactant would result in inefficiency in soil remediation by surfactant washing.

Diffusion-based calibration for solid-phase microextraction of benzene, toluene, ethylbenzene, p-xylene and chlorobenzenes from aqueous samples

Short-term solid-phase microextraction (SPME) was performed to test a recently proposed semi-empirical model for the prediction of concentrations of analyte in water samples from the fibre-extracted mass without further calibration. The mass uptake rates obtained for benzene, toluene, ethylbenzene and p-xylene (BTEX) differ considerably from the before published, showing that interfibre comparability is a serious issue. The relative prediction errors are between −55% for benzene and +82% for p-dichlorobenzene under optimal conditions, i.e. they are by an order of magnitude higher than originally published. A sensitivity analysis shows the dominant influence of the estimated thickness of the diffusional boundary layer around the fibre on the concentration predicted. Empirical modification of the model equation for this parameter yields satisfactory results under the conditions tested for both BTEX and the selected chlorobenzenes.

Impact of surface characteristics of activated carbon on adsorption of BTEX

Five residues of botanical origin were tested as potential activated carbon precursors; these are: date pits (DP), cotton stalks (CS), peach stones (PS), almond shells (ALS), and olive stones (OS). A standard activation procedure was followed (impregnation with 50% H3PO4 and heat treatment at 773 K) for the sake of comparison. Texture characteristics were determined by analysis of the N2/77 K isotherms. Highly to good adsorbing carbons were obtained in the order: PS, ALS, CS, OS and DP, respectively. Acidity/basicity characteristics were estimated by the selective titration method of Boehm. All carbons contained residual phosphates and showed high content of surface oxygen complexes mostly of acidic type. Removal of benzene, toluene, ethylbenzene and p-xylene (BTEX) was evaluated for each component in the mixture and in terms of total uptake. Low amounts of BTEX were adsorbed, which were irregularly correlated to either of the porosity or surface–chemical parameters. It is assumed that the complexity of the carbon surface with developed porosity and high content of hydrophilic oxygen functionalities determine the uptake of the hydrophobic organic molecules. In general, the order of uptake appears consistent to previous investigations as B<T<E<X, as related to decreased water solubility and increased molecular weight. A single air oxidized activated carbon at 625 K (OSA) showed a considerable reduction in porosity as well as increased acidity and improved removal capacity of BTEX per unit area.

Removal of chemical contaminants from water to below USEPA MCL using fiber glass supported activated carbon filters.

A new, low-cost fiber glass supported activated carbon (FGAC) filter has been prepared that displays enhanced adsorption characteristics for the removal of BTEX (benzene, toluene, ethylbenzene, and p-xylene) from water to below maximum contaminant level (MCL) regulated by USEPA and two chemical warfare agent simulants (diisopropylmethyl phosphonate and 2-chloroethyl ethyl sulfide) to barely detectable levels. Breakthrough curves for both the FGAC filter and a commercially available granular activated carbon (GAC) filter containing equal weights of adsorbent show that the FGAC filter has greatly improved kinetics of adsorption over the GAC filter for all six chemical contaminants. Benzene breakthrough curves showed the FGAC filter effluent to contain less than one ppb as compared to several parts per million in the GAC filter effluent. This was 2 orders of magnitude better than the GAC and represents a major advance in generating good water quality for the military as well as the general public. The FGAC filter showed a much lower pressure drop and could be completely regenerated at least 6 times by heating to 190 degrees C under vacuum.

Influence of a Nonionic Surfactant (Triton X-100) on Contaminant Distribution between Water and Several Soil Solids

The influence of a nonionic surfactant (Triton X-100) on the contaminant distribution coefficients in solid–water mixtures was determined for a number of relatively nonpolar compounds (contaminants) on several natural solids. The studied compounds consisted of BTEX (benzene, toluene, ethylbenzene, and p-xylene) and chlorinated pesticides (lindane, α-BHC, and heptachlor epoxide), which span several orders of magnitude in water solubility (Sw); the solid samples comprised a bentonite, a peat, and two other soils, which cover a wide range of solid organic matter (SOM) content. The applied surfactant concentrations (X) ranged from below the (nominal) CMC to 2–3 times the CMC. For relatively water-soluble BTEX compounds, the distribution coefficients with surfactant (Kd*) all exceeded those without surfactant (Kd); the Kd*/Kd ratios increased with increasing Sw from p-xylene to benzene on each solid at a given X, with increasing X for each compound on a solid, and with decreasing solid SOM content for each compound over the range of X studied. For the less-soluble pesticides, the Kd*/Kd ratios exhibited a large increase with X for bentonite, a marginal change (increase or decrease) for a soil of 2.4% SOM, and a moderate-to-large decrease for two soils of 14.8% and 86.4% SOM. These unique observations were rationalized in terms of the properties of the compound, the amount of surfactant sorbed on the solid, the enhanced solubilization of the compound by surfactant in water, and the relative effects of the surfactant when adsorbed on minerals and when partitioned into SOM.